1. Field of the Invention
The present application relates to a surface mountable device (SMD) type thermistor such as a positive temperature coefficient (PTC) device or a negative temperature coefficient (NTC) device. It can be applied to a printed circuit board for over-current protection and abnormal ambient temperature detection.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98.
Because the resistance of conductive composite materials having a positive temperature coefficient (PTC) characteristic is very sensitive to temperature variation, it can be used as the material for current sensing devices, and has been widely applied to over-current protection devices or circuit devices. The resistance of the PTC conductive composite material remains extremely low at normal temperature, so that the circuit or cell can operate normally. However, when an over-current or an over-temperature event occurs in the circuit or cell, the resistance instantaneously increases to a high resistance state (e.g., at least 102Ω), so as to suppress over-current and protect the cell or the circuit device.
In high density circuit design and manufacturing, it is desirable to use light, thin and downsizing surface mountable protection devices. Therefore, various surface mountable PTC devices of organic polymer are made. However, the hold currents of the PTC devices are hard to be increased due to device size limitation and poor heat transfer. Moreover, the heat insulation of the devices may cause an issue of low sensitivity to ambient temperature.